An agricultural implement is typically connected to a tractor drawbar by a clevis and tongue connection. The clevis provides upper and lower clevis members each defining a drawpin hole, and the tongue defines a drawpin hole and is inserted between the clevis members to align the drawpin holes such that a drawpin can be inserted through them and thereby connect the clevis and tongue.
The clevis may be mounted to the tractor drawbar and the tongue provided by the implement hitch, or vice versa. In either event, the tractor drawbar supports the weight of the front end of the implement being towed, which can be considerable. Thus the tongue of the implement hitch must be connected to the drawbar so that the implement tongue rests on the drawbar. Thus where a hammer strap to form the clevis is mounted to the tractor drawbar, the hammer strap is above the drawbar and the implement hitch tongue rests on the drawbar, and where the hammer strap is mounted to the implement hitch tongue, the hammer strap is under the implement hitch tongue, and again the implement hitch tongue rests on the drawbar.
A predominant area of wear on an implement hitch tongue is the front surface of the drawpin hole. It is this surface against which the drawpin bears when exerting the draft force necessary to pull the implement in the operating travel direction, and thus where full load is placed on the drawpin. Also the bottom of the implement hitch tongue rests on the tractor drawbar, often with considerable downward force. As the tractor and implement turn and pivot about the vertical drawpin, the bottom surface of the implement hitch tongue wears against the top surface of the tractor drawbar, and the drawpin wears against the front surface of the drawpin hole. As tractor and implement widths have increased, draft forces necessary to pull the implement, and in many cases tongue weight as well, have increased significantly, with a corresponding increase in hitch wear. With some implements, such as tub grinders, bale processors, grain carts and the like, while the draft forces are not excessive, tongue weight is significant and in operation the tractor and implement are constantly turning, such that wear on the bottom weight bearing surface of the tongue is pronounced.
Tractors come in a wide variety of sizes, and the drawpin hole in the drawbar of each is typically sized for a pin of sufficient strength to match the power of the tractor. Implements also come in a wide variety of sizes, and similarly have a implement hitch tongue with a drawpin hole that is sized for a pin of sufficient strength to match the power requirement of the implement. It is desirable to have the drawpin holes all the same size so that a corresponding size of drawpin can be inserted to connect the clevis and tongue in the preferred manner such that there is only minimal movement at the connection. Agricultural implement hitches are categorized by size, with a Category 3 hitch using a drawpin with a diameter of 1.50 inches and Category 4 using a drawpin with a diameter of 2.00 inches. As the diameter of the drawpin increases, the bearing surface that carries the draft force pulling the implement also increases, reducing wear. Recently Category 5 hitches have been introduced using a pin with a diameter of 2.75 inches to address the problem of increased wear in agricultural implements.
Implement hitch tongues are typically made from ductile or nodular cast iron, which is inexpensive and resists cracking, as opposed to more wear resistant materials which are brittle. It is known to temper these cast iron implement hitch tongues to resist this wear, and prolong their useful life, however such tempering significantly increases the cost of the implement hitch tongues. Similarly for increased wear resistance, implement hitch tongues can be made from cast steel, however this also significantly increases the cost.
A device called the Bull-Pull Hitch™ is available from Jenner Sales Corp. of Harristown, Ill. that addresses the wear problem by providing a bushing assembly in a hitch hole through the hitch tongue, where the required pivoting motion of the tractor drawbar and implement hitch about the vertical drawpin takes place in the bushing assembly, and not between the hitch tongue, drawbar, and drawpin as in conventional hitches.
The bushing assembly includes an outer ring with an outside surface that corresponds to a segment of a sphere, and an inner bushing that is held in the outer ring by a snap ring. The hitch hole has an inner surface that is a segment of a sphere that corresponds to the outside surface of the outer ring and opposing slots that allow the outer ring to be oriented on edge, dropped down through the slots so that the center of the spherical outside surface coincides with the center of the sphere segment on the inner surface of the hitch hole. The outer ring is then rotated 90 degrees so the outer ring is held in the hitch hole, with upper and lower edges thereof between the upper and lower surfaces of the hitch tongue substantially in the same manner as is known in the art for installing the outer race of a bearing in a bearing block.
Once the outer ring is installed, the inner bushing is inserted inside the outer ring and fastened in place with a snap ring. The top of the bushing is substantially level with the top surface of the hitch tongue, and the bottom of the bushing extends down below the bottom surface of the hitch tongue, such that the bottom annular surface of the bushing bears against the top of the tractor drawbar when the hitch tongue is connected to the drawbar with a drawpin, and the bottom surface of the hitch tongue is somewhat above the drawbar. The tongue weight thus bears down on the bottom annular surface of the bushing and creates substantial friction between the bushing and the drawbar, such that the bushing is held substantially stationary with respect to the drawbar, such that when the tractor makes a turn, the bushing assembly turns in the hitch hole. Thus there is no relative motion between the bushing and the drawbar, and so no wear takes place there.
The device is used with a clevis formed by a hammer strap on the tractor drawbar, so the drawpin is also substantially stationary with respect to the drawbar, and no wear takes place on the drawpin. A grease fitting supplies grease to the bushing assembly and reduces wear in the bushing assembly and the hitch hole.